1. Field of the Invention
This invention relates to a recording head for use in an ink jet recording apparatus which discharges ink and forms droplets of the ink and causes them to adhere to a recording medium such as paper to thereby accomplish recording.
2. Related Background Art
The ink jet recording method is a recording method whereby ink (recording liquid) is discharged from a discharge port provided in a recording head to form ink droplets, which are caused to adhere to a recording medium such as paper to thereby accomplish recording. This method has numerous advantages such as very little noise occurs high-speed recording is possible and it is not necessary to use any recording paper of special construction but recording is possible on plain paper or the like. Thus, various types of recording heads have been developed.
Regarding the ink discharge system in this ink jet recording method, mention can be made of various systems such as a system using a piezo-electric element as an ink discharge energy generating member, a system which utilizes a change in the pressure in a liquid path caused by the deformation of a piezo-electric element, or a system in which pressurized ink is vibrated by a piezo-electric element to provide a liquid droplet flow and electric charge is imparted thereto by an electrode and only those of liquid droplets which are necessary are deflected to thereby accomplish recording. Another system uses a heat generating element as an ink discharge energy generating member wherein a heat generating element is provided in a liquid path and ink is suddenly heated and liquid droplets are discharged by the force of a resultant bubble.
The typical construction of the vicinity of a discharge liquid droplet forming portion in a case where an electro-thermal converting member is used as heat energy generating means as the discharge energy generating member of a recording head is shown in the cross-sectional view of FIG. 1 of the accompanying drawings.
This recording head is of a construction in which an electro-thermal converting member having a pair of electrodes 3 formed of Al or like material and a heat generating resistance member 9 formed of HfB.sub.2 or like material for generating heat energy for discharging ink is disposed on a substrate 1 of Si or the like having its surface oxidized. A protective layer 4 formed of SiO.sub.2 or the like is provided on top of the heat generating resistance member 9 and the electrodes 3 positioned below a liquid path 6 and a liquid chamber 11 and a top plate 5 formed of resin, glass or the like in which the liquid path 6 and the liquid chamber 11 are formed is joined to the protective layer 4. (See U.S. Pat. Nos. 4,723,129, 4,740,796 and 4,417,251).
The ink discharge energy in this recording head is provided by the electro-thermal converting member having the pair of electrodes 3 and the heat generating resistance member 9 positioned between these electrodes. That is, when an electric current is applied to the electrodes 3 to cause the heat generating resistance member 9 to generate heat, the ink in the liquid path 6 near the heat generating resistance member 9 is momentarily heated to create a bubble and the ink is discharged from a discharge port 7 by a change in the volume of the ink from the momentary expansion and contraction of the volume of the ink caused by the creation of the bubble and its subsequent disappearance.
In the recording head of this type, an anticavitation layer is provided on top of the heat generating resistance member 9 and a heat accumulating layer is provided therebelow, as required. Also, in this example, the liquid path 6 and the discharge port 7 are provided in such positional relationship that the direction of flow of the ink in the liquid path 6 is the same as the direction of discharge of an ink droplet from the discharge port 7, but in some cases, these are disposed so that these directions differ from each other (See U.S. Pat. No. 4,459,600).
The recording head of the construction as described above has suffered from the problem that when a bubble remains when the ink is supplied into the liquid chamber, or when a new bubble is created during the use of the recording head and it stagnates near the opening portion in the liquid chamber in the liquid path communicating with the discharge port, unsatisfactory discharge of the ink from the discharge port occurs. Particularly, in a recording head using the heat generating resistance member as described above, the temperature of the ink in the head rises due to heat energy which has not been used for recording and gas having ink dissolved therein is sometimes discharged, and this leads to the tendency of the creation of a bubble being ready to occur.
Also, the ink jet recording head of the construction as described above is formed by a top plate which constitutes a liquid path and a liquid chamber communicating with a discharge port being usually joined to a base plate having a discharge energy generating member, but due to the structure thereof, a level difference is ready to occur in the vicinity of the opening portion of the liquid path in the liquid chamber (for example, the boundary portion between the liquid path 6 and the liquid chamber 11 of FIG. 2B of the accompanying drawings, and a bubble is liable to stagnate particularly there.
So, various means have been adopted against such stagnation of a bubble, but the fact is that a sufficient effect is not always obtained.
For example, there is a method as shown in the schematic plan view of FIG. 2A of the accompanying drawings and the schematic cross-sectional view of FIG. 2B of the accompanying drawings wherein a space 11a permitting bubbles to collect therein is provided in the upper portion of a liquid chamber 11 so that bubbles created in the liquid chamber 11 and united together and thereby increased in volume and elevated by their own buoyancy of are contained in the space 11a to thereby eliminate the influence of the bubbles upon the interior of the liquid path, but if the force with which the bubbles adhere to the wall surfaces constituting the liquid chamber and the liquid path is strong, the elevation of the bubbles by their own buoyancy cannot be expected sufficiently and a desired effect cannot be obtained.
So, there is a method wherein a pair of communication holes 10a and 10b are provided in the liquid chamber 11 so that when the head is used for recording, at least one of the communication holes is utilized as an ink supply port and when the head is not used for recording, ink is caused to flow in from one of the communication holes and ink is caused to flow out from the other communication hole, whereby an ink flow is formed between these communication holes and bubbles adhering to the vicinity of the opening portion of the liquid path 6 are removed by that flow, thereby eliminating the problem as noted above (See U.S. Pat. No. 4,380,770).
However, it has been found that in some cases, even the use of such a method cannot obtain a sufficient effect.
In order to solve such a problem, the inventor has paid his attention to the fact that in the prior-art recording head, no sufficient study has been made about the shape of the liquid chamber which takes the above-mentioned flow between the communication holes into consideration and the positional relation between the communication holes, and has carried out various studies of the shape of the liquid chamber and the liquid flow between the communication holes and as a result, has completed the construction of a liquid chamber which can effectively eliminate any bubble stagnating near the opening portion of the liquid path communicating with the discharge port which is adjacent to the liquid chamber, and has reached the present invention.